The present invention relates to aromatic copolyesters. More specifically, the invention relates to branched aromatic copolyesters which are fiber-forming, melt-processible, and in some instances are star-branched and/or capable of forming anisotropic melts. The terms "anisotropic", "thermotropic" and "mesogenic" have the same meaning and are used interchangeably herein.
U.S. Pat. No. 4,066,620, issued to Kleinschuster et al on Jan. 3, 1978, discloses anisotropic-melt-forming copolyesters of fiber-forming molecular weight consisting essentially of units derived from specified dihydric phenols and terephthalic acid or naphthalene-2,6-dicarboxylic acid. Dihydric phenol units of two different specified types are present in a mole ratio within the range of from about 85/15 to 60/40. The total of dihydric phenol units is present in a substantially equimolar amount with the acid units.
U.S. Pat. No. 4,118,372, issued to Schaefgen on Oct. 3, 1978, discloses a fiber-forming, melt spinnable (co)polyester capable of forming an optically anisotropic melt and consisting essentially of recurring units selected from
(I) --O--R.sub.1 --O-- PA1 (II) --OC--R.sub.2 --CO-- and/or PA1 (III) --O--R.sub.3 --CO-- PA1 (1) a single aromatic ring or fused, co-linear, aromatic ring system of 2-3 six-membered rings wherein chain extending bonds of the ring system are PA1 (2) an aromatic two-ring system in which individual rings are joined by a single bond or a divalent radical selected from ##STR3## and in which chain extending bonds of each ring are in 1,3- or 1,4-positions; with the proviso that one of the different recurring units is present in from about 20 to about 80 mole percent and the other different recurring units are present in a total of from about 80 to about 20 mole percent based on the total hydroxy acid units, and the total number, m, of said units per X moiety is from about 10 to about 3000; PA1 Tm=crystalline melting point; PA1 Tg=glass transition temperature; PA1 Tc=height of cooling crystallization peak.
wherein units I and II, if present, are present in substantially equimolar amounts; R.sub.1, R.sub.2 and R.sub.3 are radicals selected from (1) single and fused 6-membered aromatic carbocyclic ring systems wherein the chain extending bonds of the ring system, if attached to the same ring, are positioned 1,4- to each other, and if attached to different rings, are in positions parallel and oppositely directed, and (2) multiple six-membered aromatic carbocyclic ring systems in which the individual rings are joined by a chemical bond or a trans-vinylene group and in which chain extending bonds of each ring are in the 1,4-positions.
U.S. Pat. No. 4,161,470, issued to Calundann on July 17, 1979, discloses a melt-processible wholly aromatic polyester capable of forming a thermotropic melt phase at a temperature below approximately 350.degree. C. consisting essentially of the recurring moieties I and II wherein I is ##STR1## and II is ##STR2## and wherein said polyester comprises approximately 10 to 90 mole percent of moiety I and approximately 10 to 90 mole percent of moiety II. The reference discloses copolymers of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid.
U.S. Pat. No. 4,217,440, issued to Barkey on Aug. 12, 1980, discloses a method for preparing branched polyesters in melt or solid phase comprising (1) forming a condensation polymer by reacting together a diol, a diacid, and a polyfunctional modifier having at least three functional radicals, and (2) polycondensing said polymer in the presence of transesterification catalyst at a reaction temperature and reaction pressure effective to form a polyester of linear extension and branching, the improvement comprising polycondensing said polymer while correlating the activity of said catalyst, said temperature and said pressure to restrain the extent of reaction for said linear extension to within about 0.1% of the extent of reaction for said branching. Suitable acids include terephthalic acid and naphthalene dicarboxylic acid and suitable modifiers include trimesic acid, trimellitic acid, pyromellitic acid, and pentaerythritol.
Other patents which disclose anisotropic aromatic polyesters include U.S. Pat. Nos. 4,184,996; 4,188,476; 4,219,461; 4,242,496; 4,256,624; 4,267,304; 4,279,803; and 4,285,852.
U.S. Pat. Nos. 4,248,980-4,248,982 disclose star-block copolymers having good impact properties and clarity and containing 60-90% by weight of a monovinyl aromatic compound and 40-10% by weight of a conjugated diene of 4-8 carbon atoms, which, in each case, have an average structure of a specified general formula. The copolymers are made by a process which requires the use of (a) hydrocarbyllithium initiator to form linear segments which are ultimately coupled to a polyfunctional coupling agent, such as pyromellitic dianhydride and mellitic acid chloride.
U.S. Pat. No. 4,248,983, issued to Bi et al on Feb. 3, 1981, discloses transparent, impact-resistant, thermoplastic star-block copolymers having good impact resistance at low temperature (-20.degree. to -40.degree. C.) as well as at room temperature, said copolymer containing 60-95% by weight of a monovinyl aromatic compound and 40-5% by weight of a conjugated diene having 4-8 carbon atoms. The copolymers have a specified general formula and are made by a process which requires the use of a hydrocarbyllithium initiator.
U.S. Pat. No. 4,248,984 discloses similar star-block copolymers containing 60-90% by weight of a monovinyl aromatic compound and 40-10% by weight of a conjugated diene and having a different general formula.
British Pat. No. 1,579,779 discloses a flame retardant composition having improved melt strength for molding comprising (a) a branched, high molecular weight poly(alkylene terephthalate or isophthalate) resin having a melt viscosity of at least 15,000 poise, comprising a high molecular weight poly(alkylene terephthalate or isophthalate) and from 0.05 to 3 mole percent, based on the terephthalate or isophthalate units, of a branching component which contains at least three ester-forming groups; and (b) a flame retarding amount of a flame retardant as defined therein. Suitable branching components include trimesic acid, pyromellitic acid, and pentaerythritol.
Conventional thermotropic polyesters which are especially useful for the preparation of high-strength fibers suitable for applications, such as tire cord, cable and the like, are substantially linear, crystalline materials the strength of which can usually be improved in the fiber direction by heat-treating the unrestrained as-spun fibers. Such fibers are usually weak in the transverse direction. Thus, there is a need for polyesters which form fibers having significantly improved transverse strength properties in addition to fiber-direction properties substantially equivalent to those of conventional linear polyesters.